CVE-2015-5522 in iOS
Summary
by MITRE
Heap-based buffer overflow in the ParseValue function in lexer.c in tidy before 4.9.31 allows remote attackers to cause a denial of service (crash) via vectors involving a command character in an href.
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Analysis
by VulDB Data Team • 06/16/2022
The vulnerability identified as CVE-2015-5522 represents a heap-based buffer overflow affecting the HTML parser library tidy version 4.9.30 and earlier. This flaw exists within the ParseValue function located in the lexer.c file, which processes HTML content and handles various attributes including href values. The vulnerability specifically manifests when the parser encounters command characters within href attributes, creating a condition where maliciously crafted HTML input can trigger memory corruption. The issue falls under the Common Weakness Enumeration category CWE-121, which classifies heap-based buffer overflows as a critical memory safety vulnerability that can lead to arbitrary code execution or system instability. The attack vector involves remote exploitation through web applications that process untrusted HTML input, making it particularly dangerous in web-facing environments.
The technical implementation of this vulnerability exploits the improper handling of command characters within href attribute values during the lexical analysis phase of HTML parsing. When the ParseValue function processes an href attribute containing command characters, it fails to properly validate or limit the buffer allocation, allowing an attacker to write beyond the allocated heap memory boundaries. This overflow condition occurs because the parser does not adequately check input length or character sequences before performing memory operations. The heap corruption resulting from this overflow typically manifests as a crash during the parsing process, causing the application to terminate abruptly and resulting in a denial of service condition. The vulnerability demonstrates characteristics consistent with ATT&CK technique T1203, where adversaries leverage application vulnerabilities to cause system instability or denial of service.
The operational impact of CVE-2015-5522 extends beyond simple denial of service to potentially compromise system availability in web applications that rely on the tidy library for HTML processing. Applications including content management systems, web proxies, and HTML sanitization tools that utilize affected versions of tidy become vulnerable to remote exploitation by attackers who can craft malicious HTML content containing command characters in href attributes. This vulnerability affects not only individual web applications but also entire infrastructure components that depend on HTML parsing capabilities. The risk is particularly elevated in environments where users can submit HTML content, as attackers can exploit this flaw to crash services and potentially disrupt business operations. Organizations using affected versions should prioritize patching to prevent exploitation, as the vulnerability can be leveraged for persistent denial of service attacks against web services and applications. The remediation process requires updating to tidy version 4.9.31 or later, which includes proper bounds checking and input validation mechanisms that prevent the heap overflow condition from occurring.